Conventionally, a driving device for a hybrid vehicle has an engine and a motor. In addition to an engine as a driving source, such a driving device for hybrid vehicle is equipped with a generator motor mainly for power generation and a traction motor mainly functioning as a driving source of the vehicle.
In the above-mentioned driving device for hybrid vehicle, the engine is started with the driving force of the generator motor. Thus, in addition to a driving force transmission path for driving the vehicle that drives the vehicle by transmitting the driving force of the engine or the traction motor to drive wheels, the driving device for hybrid vehicle has a driving force transmission path for starting the engine that starts the engine by transmitting the driving force of the generator motor to the engine.
However, when starting the engine with the driving force of the generator motor, resonance may occur as the rotational speed of the driving force that is transmitted via the driving force transmission path for starting the engine passes through the natural frequency before reaching the idling speed from the start of the engine. In addition, excessive resonance may occur when this natural frequency overlaps with the natural frequency of support pans (such as a mount) of powertrain, which may generate large vehicle body vibrations due to resonance along with the addition of impact load on each part.
As conventional technologies, devices described in Patent Documents 1 and 2 can prevent the transmission of excessive torque due to the above-mentioned resonance. Patent Document 1 describes a torque fluctuation absorber installed between the output shaft of engine and the input shaft of transmission. This torque fluctuation absorber includes a damper part that absorbs torque fluctuation (or a torque fluctuation absorbing mechanism) and a limiter part that causes slippage when torque fluctuation above a certain value occurs between the output shaft and the input shaft (or a torque limiter mechanism). Patent Document 2 discloses a structure that, in a hybrid vehicle having a driving force transmission path that transmits the driving force of engine and electric motor to the drive wheels, a torque limiter mechanism is arranged inside the rotor of the electric motor installed in the said driving force transmission path, in a hybrid vehicle having the driving force transmission path that transmits the driving force of engine and electric motor to the drive wheels.